Discriminator circuit



April'29, 1947. D. D. GRIEG DISCRIMINATOR CIRCUIT Filed May 15, 1943l WM5/IMD INVENTOR 00A/#0 0. GAVE@ BY /mf ATTQRAEY Patented Apr. 29,A 1947 v DlsoanmNAToR CIRCUIT Donald D. Grieg, Forest Hills, N. Y., assignor to Federal Telephone and Radio Corporation, Newark, N. J., a corporation of Delaware Application May 15, 1943, Serial No. 487,071

4diier in amplitude from a Wanted pulse .or pulses. l In my copending application Serial No. 467,516,

led December 1, 1942, methods andmeans are disclosed for selectively ltering a wave modulated with pulses differing in amplitude so as to eliminate from the pulse modulated wave those pulses of greater and/or lesser amplitude than a wanted pulse.

Itis an object of my present invention to provide a simplified method and means in addition to those disclosed in my aforesaid copending application for selectively ltering a Wave modulated with pulses differing in amplitude.

According to my invention, a Wave modulated with pulses differing in amplitude is applied to a threshold clipper arranged to threshold clip the wave at an amplitude greater than the smaller amplitude pulses but less than the given amplitude of a wanted pulse. The wave is also applied to a second threshold clipper arranged to clip, amplify and invert in phase that portion of the wave above the amplitude of the wanted pulse. The outputs of these two threshold clippers are mixed together in a mixer tube whereby the inverted pulse energy of the second clipper subtracts from the pulse energy obtained from the iirst clipping operation whereby the output pulses of the mixer corresponding to the greater amplitude pulses are at least rendered less than the amplitude of the output pulse which corresponds to the wanted input pulse. Should there be more than one pulse in the input'wave greater in amplitude than the wanted pulse and such greater pulses also differing from each other in amplitude, it will be desirable to again threshold clip the output of the mixer stage to eliminate those pulses which correspond to the greater pulses which now are less than the pulse corresponding to the wanted pulse of the input wave,

For a further understanding of the invention, reference may be had to the following detailed description to be read in connection with the accompanying drawing, in which:

Fig. 1 is a schematic wiring and block diagram of a pulse filtering system according to my invention; and

Fig. 2 is a graphical illustration of the operating steps thereof.

Referring to the gures of the drawing, curve a of Fig. ,2 represents an input wave modulated with pulses of various amplitudes. Pulse I is Wanted pulse of a given amplitude while pulses 11 claims. (C1. 17a-giet)y prises a conventional double triode stage.

2 Il and I2 are two pulses of greater amplitud which in themselves differ in amplitude. The wave is also shown to be modulated with a pulse I4 which is of less amplitude than the wanted pulse lil. This wave is applied at the input l5 of a known threshold and amplifying clipper I6 which preferably is adjusted to clip the wave at an amplitude level Il. This amplitude level as shown on curve d is selected greater than the amplitude of pulse i4 but less than the amplitude of pulse Iii. This clipping operation results in curve b having pulses l lb, lb and l2b. The pulse i4 has been eliminated.

The wave according to curve b is applied through connection 2G `to a second threshold and amplifying clipper 22 which preferably is adjusted by control resistor 2l to threshold clip the wave of curve b at a level 23. This level 23 is greater than the amplitude of pulse lilb but less than the amplitudes of the unwanted pulses IIb and l2b. The output of the clipper stage 22 is taken from the plate connection 24 so that the upper portion thus clipped is inverted in phase as indicated by the pulse energy llc and |20 of curve c. This inverted energy is applied to an input connection 26 of a, mixer stage 3D through the movable switch contact in contact with a terminal 2 connected to a grid 3l of the mixer,

As shown in Fig, 1, the mixer stage 3D com- The output energy of the threshold clipper I6 is also applied to the mixer stage 30 through a connection 32 to a second grid. The mixer stage is preferably provided with a threshold level by the voltage developed across the resistor-condenser network R-C which serves to eliminate lower amplitude fiuctuation noise occurring between pulses. The output anode connection 36 of the mixer stage, however, is shown for purposes of illustration connected to a third threshold clipper 49, whereby a low threshold clipping level 42 operates to eliminate any pulse energy such as pulses and 50h less in amplitude than wanted pulse llld. The mixer stage, of course, may be provided with adjustable means to selectively vary the .threshold level thereof to perform the clipping operation of clipper 4U. Clipper 40 maythen be omitted.

From the foregoing description, it will be clear that the pulse energy represented by curves b and c are mixed in the mixer stage 3Q. This mixing operation causes the inverted pulse energy of curve c to cancel a corresponding portionof the corresponding pulse energy of curve y'12. This results in an output wave for the mixer substantially equal to or greater than the amplitude of the unwanted pulses andob. This, of course, will not only eliminate fromthe Wave d these pulses but also any noise uctuations that may be present thereby resulting ina' final out.

put pulse le amplified by theclipper-li and corresponding to the wanted pulse of curve a. As hereinbefore pointed out this last clipping may be performed by the mixer stage itil thereby eliminating clipper et.

.Should it be desirable toselect the greater pulse ,Il from the curved, this may be. accomplished by. adjusting the threshold clipper 22^to..clip at .a level 45 and by shifting the movable-contacts 25 andi to contacts .2t and 35 respectively. This may be done` byganging'the controls of contacts 25 and :'lflwith the adjustable Contact of resistor El as indicated bythe bro-ken line 48. This eliminates all. of the pulses `with the exception of pulse il whichby-passes the mixer V3l?.

The threshold clipper :lll in this case-'may alsobe by-passed orthe clipping functionthereof eliminated.

While I have shown the .-wave a .modulated wthpulses .having similar leading and 'trailing edges, the system will discriminate as to yamplitude for pulses having different build-up and decay times. In the latter case, the cancellation operationeel the'mixer will, of course, Vresult in a fluctuation morepronounced than the 4fluctuations `SiG-and 5th which result from cancellation ofpulses il and l2.

:Where refer YinY the description and the appended claims to pulse modulated Wave, I-:use

.this expression ina generic sense to include'trains of pulses formed -by yeither pulse modulation .of radio. frequency carriers -or vby pulse modulation of electrical currents, such, foraexample, vascii- ,rectcurrent It will therefore be clear thatmy invention is applicable to radio systems andalso .to systems using Vline transmission such, forexample,r as telegraph' systems.

While l" have described `the .principlesloifmy invention in Yconnection with a' specificsisystem, it will be clearly understood .that ithe: system herein .illustrated and describedlis "given only by Way of-.exampleand not as limiting-the scope lof my invention as` set` forth inthelobjectrand ci lated wave those pulses or" greater and lesser aniplitude than a given amplitude comprising threshold clipping the wave at an amplitude greater than the smaller amplitude pulses but less than said given amplitude, threshold clipping and inverting in phase that portion of the Wave clipped above said given amplitude, mixing the inverted pulse energy with the pulsefenergy obtained by the first-mentioned clippingfoperation, whereby the output pulses corresponding to the greater amplitude pulses are less than said given .amplitudaand .threshold clipping said output pulses toV eliminate those output pulses less than said given amplitude.

y3. A method .of eliminating from a pulse mod- .ulated wave those pulses larger than a given amplitude comprising threshold clipping and in- -verting in phasev .the'portion 0f the wave above saidzgiven amplitude, and mixing the inverted pulse energy with energy of said modulated wave whereby the output pulses correspondingy to greater yamplitude pulses are substantiallyeliminatedthereby giving a final pulse output corresponding .to those pulses of said given amplitude.

4. A method of eliminating.fromv a pulse modulated Wave those pulses larger than la given amplitude comprising thresholdclipping .and inverting in phase the portion of thewave above said given amplitude, mixing the inverted pulse energl7 with energy of saidmodulated wave whereby the output pulses corresponding to the greater amplitude pulses are atleast less than said given amplitude, yand threshold clipping 'the output oi said mixing operation tol eliminate those pulses less than saidy given y amplitude.

5. A system for eliminating froma .pulse modulated `wave those pulses of greater and llesser amplitude than a given :amplitude comprising means :tothreshold: clip .the wave at an amplitude above Vthe smaller'y amplitude lpulses .but lessthan saidgivenamplitude, means to threshold clip and invertin phase thatportion of the'wavefabove said given amplitude, .means to mix vthe vinverted pulse energy with theoutput pulse energy of said first-mentioned clipping-means, whereby the pulse output corresponding to the greater 'amplitude pulses is -at least less than saidgiven energy amplitude, and means to threshold clip the output of saidmnixing means 'to eliminate 'those pulses vless vthan said given'ampltu'de.

I6. A system for Aeliminatingv from a'wavemodulated-with Ypulses of. diil'erent amplitudes those pulses larger than a given amplitude-comprising means to .threshold clipandinvertlin .phasethat portion 'oi the .waveabove said (given. amplitude, and meansI fonmixing theinverted-pulse energy withthe wave energywherebyf-the pulse output corresponding ,to the ,greater -amplitude pulses is substantially eliminated. Y

.7. .Thesystem'dened-in claim 6, -vwherein fthe energy mixing. means includesmeansbiasing `it tto a, given .threshold level to-eliminate low .amplitude fluctuations between Vpulses foi said given -1 ampli-V tude.

8. A system for "eliminating'fromawavemodulated withpulsesloi 'different amplitudes those pulses. larger .than fa .given amplitude comprising means to threshold clip and invert in phasezthat portion of the wave.abovesaidggiven amplitude, means for mixing the inverted pulseienergyilwith the .wave energy vwhereby the foutputgpulsesicorresponding @to thexzgreater :amplitude .pulses' are less @than '-jsaid. given f amplitude, and:` means to threshold clip the output fof said .m'ixing'me'an's to eliminate those output pulses less than the pulses corresponding to said given amplitude.

9. A system for selectively ltering a Wave modulated with pulses diiering in amplitude comprising a threshold clipper means to adjust said threshold clipper to clip and invert in phase that part of the wave greater than a given amplitude, means to mix the modulated wave and the'inverted energy to obtain a pulse output corresponding to the pulses of said given amplitude, a circuit by-passing said mixer means, means for selectively applying the output of said clipper means to said mixer means and to said luy-pass means, and means ganging the selective means with the clipper adjustingr means, whereby the pulses of said given amplitude and pulses of amplitude greater than said given amplitude are selectively isolatable from said wave.

10. A method of eliminating from a pulse modulated Wave those pulses larger than a given amplitude comprising threshold clipping and amplifying a portion of the larger unwanted pulses to obtain pulse energy of the' unwanted pulses in inverted form, and mixing the inverted pulse energy with energy of said modulated Wave Wherebythe output pulses corresponding to greater amplitude pulses are substantially eliminated thereby giving a nnal pulse output corresponding to those pulses of said given amplitude.

11. A system for selecting wanted pulses of a given amplitude from a train of pulses including pulses of amplitude greater than said given amplitude comprising means to threshold clip and invert in phase a portion of the pulses of greater amplitude, means for mixing the inverted pulse energy with the Wave energy whereby the larger pulses are reduced below said given amplitude, and means to threshold clip peak portions of the wanted pulses at a level above the reduced pulses.

- DONALD D. GRIEG. 

